it's not a codec issue, it seems the videos are in a, let's say, non-standard format. not a single player or video tool can handle them (mpc, wmp, qt, vdub, ...) except for vlc (well, and mplayer, but seeking doesn't seem to work there). wtf

Excuse me, but this seems to be the only thread I can find about video playback issues. I have a question and i do not know whether i should post here. Recently I recorded a gameplay video with Fraps and later found it was too big, (the video length is just 10 minutes but the output is near 2G).So I downloaded this software as you can see (http://www.videoconverterfactory.com/tips/compress-fraps-videos.html) to help me compress Fraps videos. But after conversion, the original AVI file got converted into MP4 and I found there was some kind of quality loss and the frame rate also dropped a little. I want to know if you guys know any better parameter settings which can make it look better.

I promise that I have read the FAQ and tried to use the Search to answer my question.

I didnt look at your converter program but either you missed a setting during conversion or it is "crippleware" and will only let you save it as mp4.
There are free softwares that will do what you want.